1. Field of the Invention
The present invention relates to a new and improved light probe for a near-infrared body chemistry measurement instrument.
2. Description of Background Art
Body chemistry measurement is a health field wherein the goal is to detect, monitor, or prevent health problems due to disease, illness, or genetic propensity by measuring analytes in the body. A large and important area of interest is in developing measurement devices that are inexpensive to produce, yet give fast and reliable results. The ultimate goal is an instrument that is reliable enough for medical use, yet inexpensive and reliable enough for use by ordinary persons. Through the use of such body chemistry measurement instruments, persons will be able to monitor their own health.
Several body chemistry characteristics are vital to long term health, and are becoming easier to monitor. These are characteristics such as body fat percentage and body water percentage. Long term health can be improved by keeping both characteristics within widely-accepted ranges. It is well established that health risks increase for those who are more than twenty percent over optimal weight. Measurement of weight alone, however, is not sufficient. Body composition (i.e., body fat levels), is one preferred measure of health and fitness. Generally, body fat levels of fifteen to eighteen percent for men and twenty to twenty-five percent for women are considered acceptable. Body fat levels greater than twenty-six percent for men and twenty-nine percent for women are considered to be indicative of obesity and are a potential risk factor for the development of diseases such as cardiovascular disease, high blood pressure, and diabetes. Other important body function characteristics that often require regular measurement are blood pressure, pulse rate, blood glucose levels, etc.
Body fat testing can be measured by several known methods, such as by measurement of body part circumferences, water immersion, bioelectrical impedance, or infrared light interactance.
Each of the above measurements has particular problems or disadvantages. Measuring body part circumferences and using body fat calipers are two easy and cheap methods, but may be inaccurate due to a user's lack of knowledge on proper use, and may further suffer from differences between individuals, differences due to age, or differences due to gender. Numerous combinations of skinfold measurements taken at different sites are required. This data must be applied to regression equations to predict body fat levels.
Water immersion body fat testing is widely accepted as the standard by which other body fat testing methods are measured. A person is immersed in water and the volume of displaced water is compared to the person's weight. Water immersion tests are expensive, somewhat complicated, require relatively expensive and bulky equipment, and must be performed by trained personnel. These limitations make it impractical for general use.
Body fat composition may be measured by bioelectrical impedance, where body fat is indirectly measured by measuring the body's resistance to a small electrical current. This resistance is used to obtain body fat levels, as bones, muscle and tissue have a high level of electrical conductivity compared to body fat. In principle, the lower the electrical impedance, the greater an individual's lean body mass. This method can be incorporated into a testing device that is small and inexpensive, and available for general use. However, the accuracy of the bioelectrical impedance method can be affected by several critical factors. To make a valid measurement, the subject must be in a stable condition. The amount of hydration (i.e., the amount of water in the body) and the amount of electrolytes must be consistent every time a measurement is made. This is because bioelectrical impedance does not measure body fat, it measures the body's resistance to electrical current flow. Thus, for example, if the person is perspiring, the test results of the predicted body fat may be inaccurate. In fact, in order to obtain accurate measurements, the National Institutes of Health (NIH) insists that the person being tested with a bioelectrical impedance instrument have fasted (no food or drink) for a minimum of four hours, and preferably six hours.
Near-infrared interactance measures body fat levels by measuring the absorption of infrared light at very specific wavelengths. All organic materials (i.e., fat or protein) absorb light in unique parts of the infrared light spectrum. Body fat can therefore be accurately and quickly measured by directing selected wavelengths of infrared or near-infrared light into a test area and measuring the amount of reflected light. Hereinafter, the term "infrared" will be used to encompass infrared as well as near-infrared wavelengths. Body fat will absorb the infrared light, while lean body mass will reflect it. Infrared light measurement instruments may also be used for other body chemistry measurements, such as blood analytes (e.g., glucose, hemoglobin), percentage of muscle (i.e., protein), pulse rate, etc.
In operation, a long narrow light probe wand is connected to the infrared measurement instrument, with the light probe wand both emitting the infrared light and sensing the reflected light. The light probe wand must be used properly to avoid introducing errors into the measurement, as the operator may place the operative end of the light probe wand in a poor measurement site on the test subject or may apply an improper or inconsistent pressure on the light probe wand.
The relatively large ratio between the light probe wand length in relation to its diameter presents a problem of incorporating a light probe into measurement equipment. Automated test instruments for measurements such as blood pressure are commonly available, and are popular due to their ease of use. They commonly use a cuff in which a person inserts his or her upper arm for testing. It has been found that the biceps or triceps muscles of the upper arm are good locations for infrared measurement of body fat levels. An infrared measurement employing a relatively thin, disc-shaped light probe could be easily incorporated into an existing automated measurement instrument. It is desirable to have an infrared light probe of a size and dimension that could be used in a pressure cuff, such as in a blood pressure tester, and would therefore be easy to use, consistent, and capable of being used without the help or expense of trained personnel. An infrared light probe could therefore be included as part of a blood pressure tester or other automated body chemistry measurement.
What is needed, therefore, is a light probe method and apparatus of a small depth dimension that can be used for an infrared body chemistry measurement instrument.